Method of reeling ladder web for venetian blinds



1940- D. MURDOCK ET AL 2,225,921

METHOD OF REELING LADDER WEB FOR VENETIAN BLINDS Filed June 25, 1937 2 Sheets-Sheet 1 FREDERICK D. HVRDOCK HAHHYDEXZEI? PEG/f INVENTORS ATTORNEY 1940- F. D. MU'RDOCK ET AL 2,225,921

METHOD OF REELING LADDER 'WEB FOR VENE'I'IAN BLINDS Fiied June '25, 1937 2 Sheets-Sheet 2 [mum/6X12 170mm jammy DEXTER mm INVENTORS ATTORNEY Patented Dec. 24, 1940 UNITED STATES PATENT OFFICE Frederick D. Murdock, Pawtucket, R. I., and Harry Dexter Peck, Sharon,

Mass, assignors to Murdock Webbing Company, Central Falls, It. 1., a corporation of Rhode Island Application June 23, 1937, Serial No. 149,814

2 Claims.

This invention relates to a method of reeling ladder web for Venetian blinds.

Ladder web for Venetian blinds is a woven fabric product consisting of two main tapes and a series of interconnecting crosss traps simultaneously woven on a 100m. Each tape and strap are made individually except that at intervals the warp threads of a strap are interwoven with the filling thread of a tape in an area generally known as the stitching area. When the main tapes are spread apart, the straps form the ladder rungs upon which the slats of the Venetian blind rest. It is obvious that if these slats are to be regularly spaced in the finished blind, the spacing of the cross straps must necessarily be uniform, and since each cross strap is bound regularly to a main tape it follows that each main tape must be uniformly woven and its normal length maintained with unfailing accuracy. This is readily accomplished in the weaving of the ladder web. The difficulty of maintaining the accurate length of the main tapes is encountered when the web is wound as a roll for shipment.

For many years ladder web has'been wound in rolls on a core of about 1 /2 inches in outside diameter. Since the most of such web winds about sixteen coils or turns per inch of radius, the difference in length between the outer tape and the inner tape in any one turn is the difference in length between two concentric circles whose diameters differ by of an inch. This difference is of course pi times of an inch or .19635 of an inch. Therefore if in the winding of the web, each turn thereof must have the same length of outer tape and inner tape (and this is necessary if the web as a whole is to be maintained accurate in longitudinal dimension) it follows that there must be some adjustment made between the two tapes in each turn in order to take care of the aforesaid difference of .19635 of an inch which is a necessary consequence of the winding. Heretofore, so far as we are aware, this difference has been compensated for by attempting to stretch the outer tape of each turn to make it .19635 of an inch longer than its normal unstretched length. If such stretching can be accomplished without exceeding the elastic limit of the web no harm is done, because upon the unwinding of the roll the stretched tape returns to 50 its normal unstretched length by virtue of its inherent elasticity, and the uniformity of length of the main tapes is restored.

Ladder web, however, must in the nature of its use have a rather close elastic limit. Each web supports many slats and usually a heavierv crosspiece at the bottom of the blind. If the web is easily stretched the slats will be unevenly spaced, the distance between slats increasing from the bottom toward the top of the blind. This is not only most unsightly but prevents the slats from properly overlapping when they are tilted to shut out the sunshine or bright light. Thus it is an essential requirement of ladder web that it have a relatively low permissible stretch, for example about ,4, of an inch per inch of length. If such web is wound on a core of say 1 /2 inches outside diameter, the' theoretical center line or neutral axis of the inner tape next to the surface of the core will have a length corresponding to a circle of 1 inches in diameter or a length of 4.8106 inches. The outer tape of this first turn will have the same actual length, and if it is stretched to makeup the aforesaid difference of .19635 of an inch, it will be stretched at the rate of over W of an inch per inch. This would effect permanent distortion of the outer tape and this distortion would continue, becoming progressively less, until the roll has reached a size such that the turns. of the web are of sufficient length to permit the outer tape to be stretched .19635 of an inch without exceeding its elastic limit. Under the assumed thickness of the web and a permissible stretch of about 4, of an inch per inch, such a turn of sufiicient length would be reached when the roll has reached a diameter of substantially inches. Accordingly, heretofore in winding ladder web on small size cores of about 1 inches outside diameter, it has meant a definite loss of several yards of the web nearest to the core, in fact, that length of the web needed to reach that turn of the roll whose outside diameter is approximately 5 inches.

Our invention is directed to a new method of reeling whereby the ordinary ladder web may be wound on a core of about 1 inches in diameter without any'permanent distortion. It is a feature of our improved method that no undue strain need be placed on the web, at no time need it be stretched beyond its elastic limit. Indeed, at the very start of the winding, the web need not be stretched at all, although for the purpose of compactness it is:desirable to impose a limited tension on the first few turns. After the roll has reached a suitable size, where the outer tape of a turn may be safely stretched at least .19635 of an inch, then sufiicient tension is imposed to effect this stretching and thereby keep the two tapes uniformly smooth throughout the remainder of the roll. 1

For avoiding any under stretching or perma Cir nent distortion of the web during the first few turns, our improved method provides hollows within which the Wrinkles of the inner tape of a turn may nest and thus allow, as it were, a harmless shortening of the inner tape of a turn instead of the heretofore harmful overstretching of the outer tape. In practice, our method can best be followed by interwinding with the first few turns of a roll, a strip of corrugated paper, arranged so that the hollows between its ridges are open outward with respect to the axis of the core. As the web and this paper are wound together, the wrinkles which form in the inner tape of each turn nest into the hollows of the paper and thus permit the outer tape to wind on smoothly under a relatively light tension which does not cause even an approach to apermanent stretch in this outer tape. The strip of'corrugated paper is continued until the roll has as.- sumed a diametrical size such that the outer tape of a turn can safely be stretched at least .19535 of an inch and still be within the elastic limit of the fabric.

The best mode in which we have contemplated applying the principles of our invention is shown in the accompanying drawings, but these are to be taken as merely illustrative because it is intended that the patent shall cover by suitable expression in the appended claims whatever features of patentable novelty exist in the invention disclosed.

In the accompanying drawings:

Figure 1 is a perspective showing a portion of ladder web as it is used for Venetian blinds;

Figure 3 is a perspective of a core of 1 inches in outside diameter;

Figure 4 is a perspective of a piece of corrugated paper used in the practice of our invention;

Figure 5 is a side view of the central portion of a roll of ladder web reeled in accordance with our invention; and

Figure 6 is a view, like Figure 5, but on a greatly enlarged scale, of a vertical section through the central portion of the roll as it appears on a mandrel.

Referring now more particularly to the drawings, ladder web for Venetian blinds comprises a main tape I and another identically similar main tape 2, interconnected by a series of cross. straps 3 and 4. Both main tapes and the two straps are made at the same time on a loom, the main tapes being woven throughout their entire length. Each strap may be simply a group of parallel warp threads but preferably each strap also comprises a filling thread, and it is the latter form of strap which we have shown in the drawings.

Figure 2 illustrates how the web comes from the loom except that the main tapes are slightly separated for purpose of disclosure. Starting at the bottom of this figure, each main tape I and 2 is woven separately and there is also seen one (3) of the straps woven by itself. At regularly spaced intervals the regular interweaving of the filling thread of the strap with its warp threads ceases and for a shorter portion, generally termed the stitching area, the 100m mechanism operates thus bound to the maintapeZ.

Preferably in this stitching area, close by the termination thereof, the filling thread of the strap is also interwoven for a pick or two with the warp threads of the strap so that at the end of the stitching area, there will be but a short length of the strap filling to float with the warp threads of the strap to the other main tape I. This relatively short floating portion of the strap is designated 3b in Figure 2. Then immediately follows another stitching area 3a where the warp threads of the strap 3 are interwoven with the fiiling thread of main tape I. At the end of this stitching area 30, the filling thread (which preferably has been interwoven once or twice with the warp threads of the strap close by the beginning of the stitching area 30) is again regularly interwoven with the warp threads of the strap to form the relatively long extended portion 3d. This separate weaving of the strap and the main tapes continues until it is time to I again bind the strap to main tape 2 at stitching area (-ie, precisely as already described with respect to stitching area 3a. This cycle of operations continues throughout the length of the web. At the same time a similar cycle brings about the formation of the other strap 4 and its attachment to the main tapes at stitching areas 4a and 40 corresponding to but occurring intermediately the areas 30, and 30 already described. After a sufiicient length of the web has thus been produced by the loom, it is taken to operatives who out each floating portion 31), 3 etc. (likewise the corresponding short floating portions of strap 5) leaving the main tapes connected by the relatively long extended strap portions 3d and 4d. Thus when the Venetian blind is assembled, the tapes may be separated to receive slats 5, one of which rests on each portion 3d and id of the straps, these portions when the blind is viewed edgewise appearing as the cross rungs of a ladder. Thus far in the description no novelty has been disclosed.

The features of the present invention reside in the method of winding such web upon a small size core 6 of about 1 inches in diameter. The size of core shown for purpose of illustration is 1 inches in diameter to indicate that no specific size of core need be employed. Indeed, it is within the scope of the invention to do away with any core and wind the tape on a mandrel of a winding machine. Such mandrel may be as small as inch in diameter or any other convenient size, and when the Winding is completed the roll of tape may be slipped off such mandrel and packaged for shipment. It is preferable to employ a core, as this not only aids in maintaining the compactness and stability of the roll, but serves also as a desirable bearing when the roll is placed on a pipe or wooden axle prior to unwinding.

It is evident from the showing in Figure 1, that if the several slats are to be uniformly separated and continue parallel with one another as one tape is moved upward or downward with respect to the other, the cross straps must themselves be uniformly spaced. All of which boils down to saying that the normal unstretched length of each main tape must be maintained unchanged throughout the entire length of the web. This requirement has heretofore not been satisfied when ladder web has been wound on cores or diameters as small as 1 inches or thereabouts. This is due to the obvious fact that in winding the web at any diameter, the outer tape of any one turn must of necessity correspond to a circle of greater diameter than the diameter of the circle corresponding to the inner tape of the turn;

Ladder web is usually of such thickness that it winds on about sixteen coils or turns per inch of radius, in short is substantially A of an inch thick. With such tape, the neutral axis or theoretical center line of the outer tape of any turn will be pi times of an inch longer than the neutral axis or theoretical center line of the inner tape of the same turn, because these neutral axes are 49, of an inch apart, and the difference between the diameters of the circles representing these axes is of an inch. Since the circumference of each circle is pi times its diameter it follows that the difference between the circumferences is the difference between diameters times pi, or, to repeat, is of an inch times pi in the case of ladder web which winds on about sixteen turns per inch of radius. This, by computation, is found to be .19635 of an inch, and this difference in length between the tapes is constant for every turn of web regardless of where it occurs in the roll. Therefore in the winding of ladder web, it is elemental that in each turn of the web, there must be provisions for adjustment of the two tapes so that this constant difference of .19635 of an inch will be compensated for.

It would naturally suggest itself to stretch the outer tape of a turn and thus compensate for the difference in length between the two main tapes. This has long been attempted, and where the actual length of the outer tape is great enough to permit its being elongated .19635 of an inch without execeeding the elastic limit of the web no harm is done, because upon unwinding the roll the stretched tape by virtue of its inherent elasticity resumes its normal unstretched length. But opposed to this simple solution of the problem is the fact that ladder web must be made and is made with a very small elastic limit. This is manifestly necessary, since the web when assembled in a Venetian blind must support not only its own weight, but the Weight of the numerous slats and the usually heavier bottom bar at the lower end of the blind. If there was any appreciable stretch in the ladder web when thus in use there would be an increasingly greater space between the slats as the weight increased on each section of web between the slats. To prevent such undesirable variation in the spacing of the slats, the web must be made so that it will not stretch more than 41, of an inch per inch, and the better grades of ladder web have even a smaller limit of permissible stretch.

For example, assume a ladder Web which reels sixteen turns per inch of radius and has an elastic limit of substantially .01226 of an inch per inch of length. If such web were to be wound on a core of 1 inches outside diameter, the inner tape next to the surface would have a length corresponding to a circle Whose diameter is 1 inches. The circumference of such a circle would be 5.20328 inches long. The outer tape of this first turn of the web would correspond to a circle of 1 of an inch in diameter, whose circumference is 5.39963 inches long. Thus the difference in length between the outer and inner tapes of the first turn would be, as previously stated, .19635 of an inch. This difference in length divided by the actual length of the inner tape (which is also the actual length of the outer tape) namely 5.20328 inches will give the necessary stretch per inch of the outer tape to compensate for the difference in length growing out of the winding of the tape on a 1% inch core. This necessary stretch is found to be .03773 of an inch per inch. Since this is more than three times the permissible stretch of .01226 of an inch per inch it is obvious that if the outer tape is stretched the necessary amount to compensate for the .19635 of an inch difference in length due to winding, this outer tape will be permanently distorted. This most undesirable result is avoided by the present invention.

The essence of our invention is not to require any undue stretching of the outer tape 0 but to compensate for the difference in length of the two tapes bylpermitting the inner tape I to shorten, as it were, by wrinkling, and to provide suitable spaces wherein these wrinkles of the inner tapes may nicely nest without harm to the web. This is readily accomplished by interwinding with the web a strip of corrugated paper 1, (see Figure 4) or any similar material having hollows across it into which the Wrinkles of the inner tape may naturally nest. Corrugated paper is light in weight, inexpensive, and because of its corrugations is of very appreciable strength against a compressive strain. We have found that corrugated paper having the corrugations Ia attached to a single backing strip lb of paper is quite satisfactory for the purpose in hand.

In the winding of the web in accordance with our invention, the ends of the tapes of the web are first attached to the core by a staple 8, or tack, and then about an inch or so back of this point of attachment, the end of the strip of corrugated paper is inserted between the web and the surface of the core, the backing strip lb being laid against the outer surface 6a of the core with the corrugations outward. This provides a series of hollows 9 or cross spaces between the ridges of the corrugations opening outward toward the inner tape. The core is mounted on a mandrel 'l 0 of a winding machine and temporarily secured thereto in such manner as to be rotated thereby in a direction indicated by the arrow in Figure 6. As shown, the mandrel has a portion lOa forming a converging space between it and the inner surface Gb of the core. A suitable pin ll, either with a knurled surface or not, is slipped into this converging space and the mandrel slightly rotated with respect to the core to wedge the pin tightly betweenthem.

As the winding begins, the web and the strip of corrugated paper are coiled together on the core, there being but a light tension imposed on the web to keep the outer tape smooth and taut. In no sense is the tension great enough to stretch the outer tape beyond its elastic limit. On the contrary, at the start of the winding the outer tape is not appreciably stretched. Because of this, there is necessarily an excess of length in each inner tape of each turn. This excess assumes the form of wrinkles extending crosswise of the inner tape and as these occur they nicely nest in the open hollow spaces of the corrugated paper as indicated at w in Figure 6. Thus at the start there is no undue stretching, if any, of the outer tape, but the difference in length between the outer tape and the inner tape is compensated for by the natural rucking or wrinkling of the inner tape, and these wrinkles readily nest in the hollows of the corrugated paper without harm to the inner tape, because upon unwinding of the rolls these wrinkles entirely disappear.

This interwinding of the corrugated paper between the turns of web is continued until the roll has a diameter such that the length of the outer tape of the turn then being made is great enough to permit the tape to be stretched at least .19635 of an inch without permanent distortion. Thereupon, the interwinding of the corrugated paper is terminated and from there on the web alone is wound on the roll, there being just enough tension applied to the outer tape to stretch it sufficiently to compensate for the constant difference of .19635 of an inch between the outer and inner tape of each turn. Such stretching of the outer tape is well within its elastic limit and so as the roll is unwound, the outer tape returns to its normal unstretched length in conformity with the length of the inner tape. Thus the invention provides for winding ladder web for Venetian blinds on small cores without permanent distortion of the web.

We claim:

1. A method of reeling Venetian blind ladder web having two main tapes interconnected by cross straps which comprises starting the reeling on a core having an outside diameter at which the difierence in length between the two main tapes in the turn of web nearest said core is greater than the elastic-limit of the web and interposing between said turn and said core a corrugated strip arranged with hollows between its corrugations open toward the inner tape,

wherein wrinkles forming in said inner tape may nest, thereby permitting the outer tape to be wound without permanent distortion.

2. A method of reeling Venetian blind ladder web having two main'tapes interconnected by cross straps which comprises starting the reeling on a core having an outside diameter at which the diiference in length between the two main tapes in the turn of the web nearest the core is greater than the permissible stretch of the web within its elastic limit, interwinding a corrugated strip with its corrugations opening outward between the core and the said turn of the web and between succeeding turns of the web until the roll reaches a diameter at which the difierence in length of the two main tapes in the turn being wound is within the elastic limit of the web.

FREDERICK D. MURDOCK. HARRY DEXTER PECK. 

